1. Field of the Invention
The present invention is generally directed to the field of particle analyzers, such as flow cytometers and hematology instruments. More particularly, it is directed to processing signals from particle analyzers.
2. Background Art
Instruments are often used to detect or measure physical events and to convert the detected physical events into electronic signals. For example, a flow cytometer is an instrument used to characterize particles. In flow cytometry, the particles are made to flow in a controlled environment and are (principally) illuminated by a laser. When a detectable physical event occurs, the flow cytometer converts that physical event into an electronic signal.
The detectable physical events are often represented as time-varying pulses that appear above DC offsets and noise. The DC component of these electronic signals is often unwanted. Removal of the DC component of these electronic signals should be performed without compromising the fidelity of the time-varying component of the electronic signals.
AC coupling circuits are special circuits that remove the DC component from time-varying signals. These coupling circuits can be very simple (such as a single capacitor) or very complex. The complexity of such circuits is typically a function of the performance requirements of the measurement system. These requirements become more demanding when the input signal is a pulse rather than a repetitive signal such as a sine wave.
Existing measurement systems in flow cytometers and hematology instruments are equipped with complex restoration circuitry that restores a signal baseline. The signal baseline is a reference point; signals above the baseline are positive and signals below the baseline are negative. The restored signal is then measured by an acquisition system. In flow cytometry the results of the acquired measurement may be displayed on a log-histogram plot, which displays particle counts versus signal intensity.
Existing restoration circuitry may use a rectification technique or a noise-centering technique. A rectification technique places the system noise in the active polarity region of the reference baseline. With a noise-centering technique only half of the noise population is above the signal baseline. The other half is “buried” since the acquisition system cannot convert negative values. Existing restoration circuits typically have a single amplitude output. A problem with this type of existing restoration circuit, however, is that it may not provide the requisite dynamic range and fidelity for use in certain types of flow cytometry and hematology instruments.
Given the foregoing, what is needed are high-resolution parametric signal restorers, and applications thereof. Such high-resolution parametric signal restorers should advantageously increase the uni-polar dynamic range of input signals, while suppressing the opposite polarity signals.